Lithium ion batteries as energy-saving products, having a high specific energy, a high cycle performance, and a low memory effect, have been widely used in photovoltaic energy storage, electric vehicles, electric tools, digital products, and other industries. The lithium ion batteries with a pollution-free feature have gradually replaced lead-acid batteries. Although a single lithium ion battery has a generally improved performance, the self-discharging rate of the lithium ion batteries in a module is still uneven. Even the single lithium ion battery can be cycled over 2000-3000 times, and the performance of the lithium ion battery module may be generally decreased by 15% due to the uneven self-discharging.
In assembling of the module, the lithium ion batteries are usually screened based on the capacity difference and the internal resistance difference.